Donald Trump's presidential transition team on Saturday challenged the veracity of U.S. intelligence assessments that Russia was trying to tip the November election to the Republican. A top Senate Democrat demanded a full congressional investigation.

The CIA has now concluded with "high confidence" that Moscow was not only interfering with the election, but that its actions were intended to help Trump, according to a senior U.S. official. The assessment is based in part on evidence that Russian actors had hacked Republicans as well as Democrats but were only releasing information harmful to Trump's rival, Hillary Clinton.

The official was not authorized to discuss the private intelligence assessment publicly and insisted on anonymity.

Trump's public dismissal of the CIA assessment raises questions about how he will treat information from intelligence agencies as president. His view also puts Republicans in the uncomfortable position of choosing between the incoming president and the intelligence community.

In a statement late Friday, Trump's transition team said the finger-pointing at Russia was coming from "the same people that said Saddam Hussein had weapons of mass destruction." On Saturday, spokesman Sean Spicer told CNN there were "people within these agencies who are upset with the outcome of the election."

Spicer denied a New York Times report that Russia had broken into the Republican National Committee's computer networks. The U.S. official who disclosed the CIA assessment to The Associated Press said only that Republican entities had been targeted during the election.

Democratic Sen. Chuck Schumer, D-N.Y., said he would press for a congressional investigation in the new year. "That any country could be meddling in our elections should shake both political parties to their core," he said. "It's imperative that our intelligence community turns over any relevant information so that Congress can conduct a full investigation."

Republican Sens. John McCain of Arizona and Lindsey Graham of South Carolina have also said they plan to pursue investigations into Russian election interference. Other Republicans have played down the reports. Texas Sen. John Cornyn wrote on Twitter Saturday that Russian hacking had been going on for years. He said the matter was "serious, but hardly news."

There was no immediate official response from Moscow. But Oleg Morozov, a member of the foreign relations committee in the upper house of the Russian parliament, dismissed the claim of Russian interference as "silliness and paranoia," according to the RIA Novosti news agency. Morozov described the allegations as an attempt to force the next administration to stick to Obama's anti-Russian course.

The investigation ordered by Obama will be a "deep dive" into a possible pattern of increased "malicious cyber activity" timed to the campaign season, White House spokesman Eric Schultz said Friday, including the email hacks that rattled the presidential campaign. It will look at the tactics, targets, key actors and the U.S. government's response to the recent email hacks, as well as incidents reported in past elections, he said.

The president ordered up the report earlier in the week asked that it be completed before he leaves office next month, Schultz said.

"The president wanted this done under his watch because he takes it very seriously," he said. "We are committed to ensuring the integrity of our elections."

The Kremlin has rejected the hacking accusations.

In the months leading up to the election, email accounts of Democratic Party officials and a top Hillary Clinton campaign aide were breached, emails leaked and embarrassing and private emails posted online. Many Democrats believe the hackings benefited Trump's bid.

Schultz said the president sought the probe as a way of improving U.S. defense against cyberattacks and was not intending to question the legitimacy of Trump's victory.

"This is not an effort to challenge the outcome of the election," Schultz said.

Obama's move comes as Democratic lawmakers have been pushing Obama to declassify more information about Russia's role, fearing that Trump, who has promised a warmer relationship with Moscow, may not prioritize the issue.

Given Trump's statements, "there is an added urgency to the need for a thorough review before President Obama leaves office next month," said Rep. Adam Schiff, D-Calif., senior Democrat on the House intelligence committee. If the administration doesn't respond "forcefully" to such actions, "we can expect to see a lot more of this in the near future," he said.

The White House said it would make portions of the report public and would brief lawmakers and relevant state officials on the findings.

It emphasized the report would not focus solely on Russian operations or hacks involving Clinton campaign chairman John Podesta and Democratic National Committee accounts. Schultz stressed officials would be reviewing incidents going back to the 2008 presidential campaign, when the campaigns of Sen. John McCain and Obama were breached by hackers.

Intelligence officials have said Obama and Republican presidential nominee Mitt Romney were targets of Chinese cyberattacks four years later.

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Associated Press writers Kathleen Hennessey in Washington and Vladimir Isachenkov in Moscow contributed to this report.